jimmyz74

I put a 450hp 383 in a 76. I have a new aluminum radiator and stock l48 hood. The problem is when the car gets warmed up it flubbers at high rpm and the tach only climbs to 2500. When the car is cool no problems. Temp gauge shows engine temp at just over 180. I was thinking it was getting so hot under the hood of was messing with the hei. Got so hot it burst an a.c. line without the a.c. running. Any ideas?

doorgunner

Buy an inexpensive infrared temperature gun and check the thermostat housing temp/radiator temp/carb body temp when the engine begins to act up to see what the actual coolant temperature is (just in case the temp dash gauge is wrong).

7T1vette

Look for locations that your fuel could be getting hot before reaching the carb. Sounds like a vapor lock issue. Ethanol fuel boils earlier than all-gas. Insulate metal fuel line to carb; thermal barrier or heat shield at carb; return fuel line added; etc.

jimmyz74

I was wondering about the fuel. But why would the tach not read over 2500 when it is heated up? I know the actual rpm is much higher. When it's cool it reads fine. Thanks for the thoughts on the super heated fuel.

augiedoggy

dumb question but did you use the correct temp sending unit? they are unique to certain years I believe..

dmruschell

The original tachometer in my 79 wasn't reading the correct RPM. I had the board replaced, and that didn't fix the issue. The vendor that sold me the board even had me send it to them, and it was accurate on their test rig and didn't seem to believe that the internals of the tach itself had gone bad.

When the car was first started, it might read ok, but within 5 minutes, it would read very low. The last time it was in the car, at highway speeds (around 3,000 RPMs), the tach was reading 800 RPMs. Replacing the tach with a new reproduction unit fixed it.

This is assuming that the engine is running OK at high RPMs and the tach is just malfunctioning.

What carb are you running? With a high performance 350 and headers in my 79, my Holley was percolating like crazy while driving. If it's getting so hot that fuel is boiling into the intake while running, that would cause the engine to not run quite right.

7T1vette

You indicated that when hot, "the tach only climbs to 2500". You didn't indicate with your first post that you were sure that the rpm read was much lower than actual. I assumed that you had a 'fuel boiling' problem that prevented the fuel from vaporizing properly in the carb and that the engine really wasn't revving higher than 2500 rpm.

If the problem is that the tach doesn't read correctly when the engine is hot, you likely have a wiring or contact problem with tach signal (under the hood). It could also be the circuit board. Not sure that the tach itself would be the issue...but anything is possible.

jimmyz74

I thought it might be getting so hot in the engine bay that it was affecting the hei? The carb is a quick fuel 750 double pumper. I did a lot of research on the temp sending unit before installing a new one, I believe it is scaled correctly. I have a temp gun and will use it the next time I have the car out. Any ideas on how to cool the compartment down? I am debating a stinger hood to force some air in and electric fans.

7T1vette

First, you need to determine how hot the compartment is getting. The engine is going to run close to 200*F anyway. Then, you have the headers/manifolds adding more heat. All the ignition components SHOULD be able to handle close to 300*F without problems. More than that???...problems could arise.

The '76 car has less airflow going through the engine compartment...by design. Remember, it didn't have any 'high perf' engines available at the time (no BB, anyway); so the side openings were rather small for good ventilation.

A stinger hood might be just the thing, if you really are running very warm. But, that incoming air still needs a place to go. If you really have a heat problem, hood [air] scoop AND openings to get hot air OUT will be needed.

Ranger24

I had a similar issue with my under hood heat after my motor was rebuilt and reinstalled in the car (burn your hand on the brake MC, hood strut etc.). I have a lot of after market parts on the car to include the aluminum rad/ e fans etc. In any event, the Dougs headers/sidepipes that we installed were only painted. After running some basic diagnostics (carb, intake etc.) I decided to send the headers and pipes out to JetHot in OKC. They applied their hightemp 2500 coating to the headers down to the rails and then the 1300 from there out to the tip of the side pipes (we did this because the 2500 has a rough finish and 1300 has a nice satin finish).

When we got the car back it was an amazing transformation. Under hood heat gone and now the sidepipes don't get nearly as hot (at least they don't leave a mark...still will make you jump if touch em getting out).

Total cost with shipping was ~$1,500. BTW - reason we shipped to OKC is because the NC shop does not apply the 2500 coating.